This application is a 371 of PCT/GB98/02690, filed Sep. 7, 1998.
1. Field of the Invention
This invention relates to a method for assaying a substance which is present in a very low concentration. Specifically, this invention concerns a method which employs catalysis to amplify a signal. The method is especially suited to biological assays. The invention has the further advantage that it allows the simultaneous assay of a mixture comprising a plurality of substances, even when these substances are present in very low quantities.
2. Description of the Related Art
Biological assays must often achieve a sensitivity to target molecules in the low femotomolar to attomolar range. Assays based on ligand binding can achieve this but often require signal amplification to indicate the success of the ligand binding in a detectable manner. Radio-isotope labelled ligands can achieve this but there are safety implications in using radio-active agents which makes them dangerous and expensive to use. Furthermore, since there is no trivial or cheap way to differentiate between different kinds of radiation, only one radiolabelled ligand can be used in any one assay.
Colorimetric, chemoluminescent assays and fluorescence based systems permit signal amplification in a variety of systems, however the number of labels that can be used simultaneously is limited due to spectral overlap effects of emission based systems.
An object of the present invention is to solve the above problems. Accordingly, the present invention provides a method for assaying a substance, which method comprises contacting the substance with an assay agent comprising a catalytic agent to associate the substance with the catalytic agent, contacting the resulting associated substance with a label precursor, and detecting a label, wherein the label precursor is capable of reacting catalytically with the catalytic agent to release the label, and wherein the label is a mass label.
The present invention also provides a kit for assaying a substance, which kit comprises an assay agent comprising a catalytic agent, and a label precursor capable of reacting catalytically with the catalytic agent to release a label, wherein the label is a mass label.